Thermodynamic and Elastic Properties of Magnesite at Mantle Conditions: First‐Principles Calculations

Abstract

Magnesite (MgCO3) is a likely main host of carbonates in the mantle and plays an important role in the transport and storage of carbon in the Earth's mantle. Its physical properties at high pressure and high temperature (PT) are crucial for understanding the deep carbon cycle. Here we investigated thermodynamic and elastic properties of magnesite under the mantle PT conditions using first‐principles calculations with local density approximation (LDA). Magnesite has the seismic velocities close to those of forsterite. The effect of the magnesite on seismic velocity of the carbonated peridotite and eclogite is subtle in the upper mantle. However, magnesite has much smaller seismic velocities and far larger elastic anisotropy than major minerals in the transition zone and lower mantle. The enrichment of magnesite in the transition zone and lower mantle will likely produce seismically detectable low‐velocity zone and velocity anisotropy.

Comprehensive Density Functional Theory Studies of Vibrational Spectra of Carbonates

“…Thus, the average root-square deviations for eight IRS-active wavenumbers obtained by the B3LYP method for magnesite and determined experimentally in [ 92 ] and [ 58 ] do not exceed 4.0% and 3.3%, respectively. There is also a good agreement with the calculated data of the authors of [ 93 ] (4.7%) and [ 94 ] (3.5%). The root-mean-square deviations for the wavenumbers of five vibrations active in RS, obtained by the B3LYP method in this work, are 1.3% (1.0%) in the experiment in [ 95 ] for magnesite (calcite), 1.5% (1.4%) for the experiment in [ 58 ], 1.6% (1.1%) for the experiment in [ 61 ], and 1.6% (1.7%) for the experiment in [ 73 ].…”

“…There will be 24 internal modes, eight of the ν 4 and ν 3 types, and four of the ν 2 and ν 1 types. The available experimental and theoretical data on vibration spectra of the carbonates under consideration are summarized in Supplementary Materials [ 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 ].…”

First-Principle Studies of the Vibrational Properties of Carbonates under Pressure

“…Thus, using the described calculation algorithm and the ν ( P ) numerical dependences from [ 9 ], for the 0–12 GPa pressure range, v T (cm −1 ) = 212 + 4.213· P − 0.076· P 2 (0.999) is obtained. There is also a satisfactory agreement for the Gruneisen mode parameters obtained earlier experimentally in [ 20 ] and theoretically in [ 10 ].…”

“…Further, high pressure Raman spectroscopy up to 27 GPa was used to study a single crystal of magnesite in [ 9 ], and it was shown that the wavenumbers of all single-degenerate modes increased almost linearly with the increasing pressure. The first-principle studies of thermodynamic and elastic properties of magnesite under pressure were held in the local approximation (LDA) DFT in [ 10 ]. Raman spectroscopy, in combination with X-ray diffraction and DFT calculations, was used in [ 11 ] to establish the magnesite phase stability.…”

Raman signatures of the distortion and stability of MgCO3 to 75 GPa

“…Geochemical and petrologic evidence indicates that carbon is subducted mainly as carbonates (e.g., Plank and Manning, 2019;Sanchez-Valle et al, 2011), potentially contributing to the deep carbon storage as well as affecting the physical and chemical properties of the Earth's interior. The presence of carbonates can dramatically affect the behavior of mantle aggregates such as melting, viscosity, electrical conductivity, thermal conductivity, and elasticity (Fu et al, 2017;Gaillard et al, 2008;Yao et al, 2018). The stability of carbonate minerals at high pressure is thus crucial to constrain the deep-carbon cycle as well as the chemistry and dynamics of many geological processes (Fu et al, 2017;Isshiki et al, 2004;Liu et al, 2015;Sun et al, 2020;Yao et al, 2018).…”